Polycarbonate resins are excellent in heat resistance and mechanical properties and therefore widely used as automobile materials, electrical and electronic device materials, housing materials, and other industrial materials for making parts and components, by way of example. Products including these resin molded articles are required to have flame retardancy in terms of safety for the purpose of fire prevention at high temperatures. In particular, flame-retarded polycarbonate resin compositions are preferably used as casings and interior parts for OA and information appliances such as computers, notebook personal computers, mobile phones, printers, copying machines and so on.
As means to impart flame retardancy to polycarbonate resins, conventionally widely known are techniques to blend polycarbonate resins with halogen-containing flame retardants such as organic bromine compounds.
However, resin compositions obtained by blending polycarbonate resins with halogen-containing flame retardants may have reduced heat stability and may also cause the corrosion of screws and/or dies in molding machines during molding process. Moreover, in the case of using halogen-containing flame retardants, gases containing the halogens may be generated upon burning, and environmental pollution may also arise as a problem during disposal and collection of products. For these reasons, there has been a demand for flame retardation without using any halogen-containing flame retardant.
On the other hand, as techniques to impart flame retardancy without using any halogen-containing flame retardant, those using phosphorus-containing flame retardants in polycarbonate resins are now being studied extensively. As phosphorus-containing flame retardants, phosphate esters, ammonium polyphosphates and so on are known. As for polycarbonate resin compositions blended with phosphorus-containing flame retardants, Patent Document 1 is known, by way of example.
However, techniques to blend polycarbonate resins with phosphorus-containing flame retardants have a drawback in that impact resistance inherent to polycarbonate resins is greatly reduced, although it is possible to obtain polycarbonate resins with high flame retardancy and good fluidity.
Phosphazene compounds containing nitrogen and phosphorus (e.g., aryloxyphosphazenes, alkoxyphosphazenes, thiophosphazenes, halogenated phosphazenes, and phosphazene polymers derived from these compounds) are useful compounds for use in flame retardants, lubricating oils, fire-resistant electrolytes, carcinostatic agents and so on, and have been studied in various fields. Particularly in recent years, phosphazene compounds have received attention because of having not only a high phosphorus content, but also high heat resistance, hydrolysis resistance and flame retardancy; and there have already been proposed some techniques using phosphazene compounds for flame retardation of resin compositions (e.g., Patent Document 2).
On the other hand, in recent years, organic sulfonic acid metal salt compounds, typified by organic sulfonic acid alkali metal salt compounds and organic alkaline earth metal salt compounds (see, e.g., Patent Documents 3 and 4), have been studied extensively as useful flame retardants.
Moreover, as one of the applications of these flame-retardant polycarbonate materials, battery packs obtained by injection molding of the resins are known (see, e.g., Patent Documents 5 to 8). In response to recent reductions in the size and thickness of products, there has been a demand for smaller sized battery packs with large capacity. For this purpose, battery pack cases used to hold batteries therein are required to have thinner walls. However, injection molding commonly used for their production requires extremely high fluidity, and materials based on the combination of currently used phosphorus-containing flame retardants and polycarbonates are not sufficient to achieve the balance of fluidity, strength and heat resistance and therefore cannot be used as products.